Volume conduction effects in tDCS using a 1mm geometry-adapted hexahedral finite element head model.

Despite of the recent progress, the knowledge about the underlying mechanisms behind tDCS is still limited. In order to gain insight in the sophisticated interplay of stimulation, volume conduction and resulting cortical current density distribution, we follow an effect-by-effect approach. We start our investigations with a homogenized isotropic three compartment (skin, skull, brain) head model, where results are still rather obvious. In each consecutive step, we then extent our head model by one additional effect, which is either a tissue layer or an anisotropic instead of a homogenized isotropic tissue compartment. For each additional effect, the resulting changes in the current density distribution are deeply investigated. Our most realistic volume conductor contains six tissue compartments and brain anisotropy (Olesch et al., 2010; Wolters et al., 2006; Wagner, 2011).